1. Field of the Invention
The invention relates to an efuse device, and more particularly to an efuse device sharing a blow device in read and write modes.
2. Description of the Related Art
FIG. 1 shows a conventional efuse array. Referring to FIG. 1, a 4×2 efuse array 10 is given as an example. The efuse array 10 comprises cells (referring to fuses 100-107) and blow transistors T100-T107. Each of blow transistors T100-T107 is coupled between one cell and a reference voltage. When one cell is determined to be blown in a write mode, the corresponding blow transistor is turned on, and a pad P10 is coupled to a high voltage level, so that a blowing current on a source line SL is provided to the determined cell to blow it. For example, in the write mode, if the fuse 100 is determined to be blown, the blow transistor T100 is turned on, and the blowing current on the source line SL is provided to the fuse 100, so that the fuse 100 is blown (or programmed).
FIG. 2 shows one fuse and a conventional sensing circuit in an efuse device, and the fuse 100 is given as an example in FIG. 2. A sensing circuit 2 comprises a reference resistor R20 and a determination unit 20. The reference resistor R20 has an impedance, and is used to be compared with the impedance of the fuse 100, so that the determination unit 20 determines whether the fuse 100 has been blown or not according to the comparison result in a read mode. Referring to FIG. 2, in the read mode, the blow transistor T100 is turned off, and the pad P10 is coupled to a ground terminal outside of the efuse device. The ground terminal provides a reference voltage for the determination unit 20, so that the determination unit 20 can determine whether the fuse 100 has been blown or not according to the impedances of the fuse 100 and the reference resistor R20. However, if the pad P10 is grounded through an additional switch in the read mode, a slight voltage level may appear on the pad P10. Thus, the Pad P10 is not ideally grounded, which may affect later sensing operation. In other words, the level of the reference voltage undesirably drifts. Thus, the sensing circuit 2 cannot correctly determine whether the fuse 100 has been blown or not.